Aircraft-propeller



1. DE W. 'HIL'L.

. AIRCRAFT PROPELLEH; APPLICATION man uuznwsra.

Patented 1m 27,1921.

7 3 SHEETS-SHEET l- 1. DE W. HILL- AIRCRAFT PROPELLER- I APPLICATION FILED mwzz. ms.

- Patented D00. 27, 1921.

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. Specification of Letters Patent. I

'mmem Patented mead, 1921 Application filed layer, 1919; derail ra aoaou.

To all whom it may concern.'.

. Be it known that I, JAMES DE Wm HILL,

a citizen of'the United States, and res dent of the city of Scottdale,

' new and useful Improvement in Aircraft- Propellers,

In, air craft propellers now in common use, the-portions 'of the blades near the propeller hub are placed at pitch angles unfavorable to the production of thrust, and the blades themselves have fixed pitch angles.

' One object of my invention is to increase the efiiciency of the propeller by the inner or and providing these bifurcated portions with a reverse camber and a negative angle of incidence so that the resultant pressure the propeller instead ofaresistance thereto "as, in the'types now in common use.

Another object of my. invention is to increase the efficiency of the propeller by providing propeller blades capable of being ro- 1 tated to a limited extent on their longitudinal axes", to vary their pitch angle, which ares are inclined outwardly and forwardly with respect to a plane normal to the axis of rotation of the propeller, said blades being provided with trailing means'forming an integral partof the blades for automatically varying the pitch angle of the blades to suit different speeds of the air era-ft, thus 86 permitting the propeller to work under the conditions and also obtainpossible flexibility. of power most favorable ing the greatest application. p Practical embodim nts of my invention in the accompanying drawings m which,

Figure l represents .one form of-my improved a1r craft elevation and part 2 represents y 1n section.

the same in top plan. 1g represents a section taken in the 9 a e .of the line IIIIII of Fig. 2.

- 1gs..4 tions taken intheplanes of the, lines IV to XII inclusive of Fig. 2.

, Fig. 13 represents another I improved propeller partly in frontelevation and partly in section.

Fig. '14 represents the same 1n top plan Fig." 15 represents a detall cross seetlon taken in the plane of the line XV--XV of Fig. 13.1. a I

county of Wyoming, l5 and State of Pen-nsylvania,ihave invented a of which the following isa specirevolution of ropeller partly in front to 12 inclusive represent cross sec form of my.

a Dotted line av -a Fi .l Fi 16 represents adetail view of the sync ronizing caring which connects the twp propeller bfade' shafts. V i

1 matic yie ws ilus'trating certain features of the invention. 1

j The propeller shaft is denoted by 1. The propeller 1 hub is fixed to rotate with the shaft land is-herein-shown as comprising two transverse sections 2 and. 3 secured together by means of bolts 4.

Instead of the usual thick blade section near'the hub,'the'blade 5 is bifurcated at its inner or hub end, the bifurcated portions 6 bifurcating hub ends of the propeller blades and 7 having a reverse camber and negative angle'of incidence. These bifurcated portions are connected adjacent to the hub by a bridge .8 from which a shaft 9 extends into the hub where it 'is suitably mounted to rotate in antifriction bearings 10, 11. In the form shown in Figs. 1 and 2, these blade shafts 9 are provided with spiral gears 12, which mesh with a spiral gear 13 loosely -mounted on the propeller shaft 1 so that the propeller blades 'are -icaused to rotate synchronously on their ldngitudinal axes, to

various pitch angles.

he rotary movement of these blades to vary-their pitch angles, is limited, as for instance, by providing the gear 13 with lugs 14 located in elongated recesses 15 in thehub. The end walls of these recesses serve as stops to keep the pitch angle of the blades within predetermined limits. The trailing blade member 16 is integrally connected to the blade 5 by. one or more rigid arms 17.

In the form shown v in Figs. 13, 14 and 15, the'propeller blades are not connected to move synchronously but each of the blade shafts 9 is provided with a lug 18 located in a recess 19, the end walls of which recess serve as stops to-limit the rotary movement of the blade between certain predetermined pitch angles. a

Light springs 20 are located upon oppo site sides of the lug18 in recesses 21 for nor mally holding the blade at an intermediate pitch angle, said springs acting as buffers to prevent liability of breaking or distorting the blade when subjected to the strain of starting and stopping.

g. 2 designates the axisfon whichthe blade revolves and dotted line 3 designates theaxis on which the blade rotates to a limited extent. The axis y-y does "not necessarily pass through the g s. 17, 18i 19 and 20 representdiagram axis 00-01:. The axis y--y'is shown as in clined outwardly and forwardly with respect to a plane normal to the axis of rotation of the propeller to. give the blade an angular setting as shown by the angle y-0j (Fig. 2).

The blade 1s arranged to have as nearly as possible; its center of gravity and center of pressure lie in the line In Fig. 3, the pitch angle is denoted b P- and the angle of incidence by I. It is c ear that the blade at this point will meet the thrust is produced by the efiicient thrust producing portions of the blade, and by this indirect method, the whole area of the blade is made to work at efficient and economical angles.

If we take the given pitch angle of any standard propeller at the blade tip and examine the sections from there toward the hub, we find that the angles gradually increase and approach a limit" that would be 90 at the propeller axis. Until these angles attain a value of or a value somewhat greater than 45, they may be called favorable angles for producing thrust. From this point the blade sections would have angles that would be called unfavorable, and as the pitch of the propeller is increased (and this design applies particularly to propellers of comparatively high pitch) this point of division between the two classificaponents. In passing fromA to C the ratios tions moves outward toward the tip.

In Fig. 17 A, B and C are blade sections: A at the tip, B at the positionhaving a pitch angle of 45, and C a section of the hub ortion. The pitch ratio of this particular ayout is 2 to 1.

For convenience, the resultant pressures R--1, R-2 and R3 are assumed to be equal. T-'-1, T2, T3 are thrust com-.

show a considerable decrease, while the ratios resultant pressures Il -1, R2, R3, and.

since they lie in the plane of rotation they must constitute a resistance to rotation. Therefore, since T-3 is of so little value, and 8-3 is a waste of effort, it would seem that possibly the resultant R3, or the power that produces it, might be used to better advantage.

In Fig. 18 O X is the axis of a ropeller, and C is a section of the hub portion of the blade as viewed from the tip. N O is tangent to the spiral flight path of the section and shows the instantaneous direction of the relative wind. The pitch angle is 73, corresponding to that of C in Fig. 4 and the angle of incidence, (or angle of attack) is 2. The resultant pressure R-3 is assumed perpendicular to the chord. 8-3 and T-3 are its components, T-3 being the thrust. Fig. 19 shows a similar lay-out, except that here the camber of C is reversed and the angle of incidence is negative, causing the line of the resultant pressure to move through 4 about 0.

Referrin to Figs. 18 and 20 C is a section of the usua propeller and in Fig. 19 C is a corresponding section'of the propeller described in my application. In both Figs. 18 and 19 0 travels on O N at the same speed, so the same power is required in either case, and since the angles of incidence are equal, the resultants R-3 and R are equal, R-3 is the result of direct propeller action, while'R (and its components F and G) is the result of a secondary application of power. This power is applied to the blade and the outer portions of the blade, whose efficiency .may be assumed at produce thrust, a part of which is used to drive C forward. This means that F and G represent 85/100 of the power necessary to produce them, therefore in summing up the gains and losses in power units resulting from this change in design, their power equivalents should be used, G then becomes Ga; 135 and F becomes F9; in the graphic representation used.

T-3 represents a useful quantity of thrust, and when G is changed to its position in Fig. 19, T3 is lost, soon the line L marked, Losses, lay off the length T-3.

.S-3 is a resistance to rotation and since its removal amounts to a gain, lay off S3 on the line M. In Fig. 19 G is a resistance to forward travel, so it must be called'a loss.

-Lay off its power equivalent Gas on L. F is an assistance to rotation, and the vector showing the useful fraction of its power equivalent has a length This 11 ntity represents a gain, so lay it off on M. Subtractthe losses from the gain 8'5 ing member travels i of the design is I minimum by inclinin production 0 as indicated by the dotted line J-K, then K Y represents a definite number of power units now available for, and automatically applied to, the thrust producing outer portion of-the blade. 4

An examination of these pressure reactions on each succeedin' section of the blade from. the hub towar the tip shows a gradual decrease in the uantity X Y. Beyond the pointjonthe b ade at which X, Y equals zero it is not profitable to reverse the camber of the sections. The result of this act-ion is purely a in in propeller efiiciency and in no way. a ects the amount of power applied at the propeller shaft. The object to secure a cooperation of Fressures'on the blade for the greater thrust.

With reference. to the advantage of providing means for automatically varying the pitch angle, the following explanation is given: v a

It will be seen that centrifu al force tends to throw the freely movable blade with'its trailing member into the plane of propeller rotation. This tendency is reduced to a the longitudinal axis outwardly and forplane normal to the propeller sufficient to the effective of the propeller bla e wardly with respect to a axis of rotation of the bring the plane of osclllation to a position center of of least departure from coincidence with the path of rotation of the center or concentrated weight of the trailing member. "The" concentrated weight of the trailapproximately on the surface of an ima inary cylinder'whose axis corresponds to the axis of the propeller shaft. 7 g

The centrifu a1 force which tends to throw the free y movable blade with its trailing member'into the planeof ropeller rotation will tend to cause the bla tate on its axis in one direction, and on account of the angular setting of the blade w1l1 also tend tocause a departureof the gravityor concentrated weight of I the trailing -member from its centrifugal locus in such a direction that there is a tendency to swing the trailing member in a dlrection opposite 'to that of the blade. Ifthen the. magnitudes of these two acting forces are equal they'ma be said to balance each other and thus al ow the blade and trailing member to lie properly on the flight path. We may assume that the blade is balanced We will then take a point W and assume that the weight of-the entire trailing blade member is concentrated at that point. When the blade at the given pitch angle is revolved about the axis w--w,

the point W will .d

ascribe a circle 'W- "(Fig. 1? and when'givenform and motion a strai g 1t line through this point parallel of gravity e to ro-- to the axis 4v-:v face. I

When the blade isaxis, the W-R' Fig. 3).

In or generates a cylindrical surrotated on the 9,-1/

the circle or an are of the circle WR' shall coincide with the cylindrical surface W,-R

within the limits X'--X (Fig. 3)..

For all practical pur o'ses this is accomplis'hed by the articulation of the yy axis point will describe a circle.

or to neutralize the influences of centrifugal force on W it is necessary that as described and shown in Figs. 1 and 2. p

in Fig. 3 indicate the variation in pitch angle of the so that when the trailing member lies on the flight path the blade is held on its given angle of incidence, the conditions necessary for efficient blade action are fulfilled.

The trailing blade member may be of such form and size with respect to the blade area.-

as may be found advisable. Likewise its location with respect to distance from propeller shaft and its distance'from the blade may be those found most desirable.

have shown one" form in which the propellerblades are synchronized and another form in which they are not synchronized, but may be permitted to act independently.

The reverse camber feature of the blade I is especially applicable to propellers mounted so that the central. ortionof the thrust area of the propeller is not obstructed by large bodies such a diators, etc.

Fromthe above description it will be seen that by the provision of reversed camber sections near the inner ends of the blades, all

' l 00 s engine housings, ra-

portions of the blades may be made to work at more effective angles, thereby materially v increasing the efliciency of the pro eller. Furthermore, this may be done 'wlthout weakening the propeller.

By providing a variable pitch for the-propeller blade, a maximum efiiclency may be obtained regardless of forward speed and also the 'full power of the motor or any portion thereof may be used at any time regardless 'offorward speed, thus givmg a great advantage climbing.

It is evident that various changs ma be resorted toin the form, construct on and ar- ,rangement of the several arts without departing from the spirit an scogeof my invention,'hence I do not wish to e limited t the particular construction and described, "but herein shown What I claim is:

1. A propeller blade having a reverse camber and a negative angle .of incidence at its inner end- 2. A propeller blade having a bifurcated inner end, the bifurcated portions having a reverse camber and a negative angle of incidence.

3. In a propeller, a'hub, and bladeshaving a reverse camber and a negative angle of incidence adjacent to the hub.

4. In a propeller, a hub, and blades having bifurcated portions adjacent the hub,

its own longitudinal axis which is inclined outwardly and forwardly with respect to a plane normal to the axis of rotation of the propeller, said blade having an excess weight on-the trailing side of its longitudinal axis andyielding means to normally hold the blade at an intermediate pitch angle.

.-7. A propeller blade freely rotatable on ,its own longitudinal axis which is inclined outwardly and forwardly with respect to a plane normal to the axis of rotation of the propeller, said blade having an excess weight on the trailing side of its longitudinal axis and means for limiting the pitch varying movement 'of the blade.

8. A propeller'blade freely rotatable on its own longitudinal axiswhich is inclined outwardly and forwardly with respect to a plane normal to the axis of rotation of the propeller, said blade having an excess weight on the trailing side of its longitudinal axis,

means for limiting the pitch varying movement of the blade and yielding means to normally hold the blade at an intermediate pitch angle.

9. A propeller blade freely rotatable on its own longitudinal axis which is inclined outwardly and forwardly with respect to a plane normal to the axis of rotation of the propeller, and a trailing member forming an excess weight on the trailing side of the longitudinal axis of the propeller blade.

' 10. A propeller blade freely rotatable on its own longitudinal axis WhICh is inclined outwardly and forwardly with respect to, a plane normal to the axis of rotation of the propeller, and a separated trailing member whose center of gravity is located at a point on the trailing side of the longitudinal axis of the ropeller blade.

11. propeller blade freely rotatable on its own longitudinal axis which is inclined outwardly and forwardly with respect to a plane normal to the axis of rotation of the propeller, and a separated trailing member whose center of gravity is located at a oint .onthe trailing side of the longitudina axis of the propeller blade between the blade and trailing member.

12. A propeller blade freely rotatable on its own'longitudinal axis which is inclined outwardly and forwardly with respect to a plane normal to the axis of rotation of the propeller, the center of ravity and center of pressure of said bladeIying substantially in said longitudinal axis," and a trailingi member whose center of gravity is locate on the trailin side of the longitudinal axis of the propel er blade.

In testimony, that I claim theforegoing as my invention, I have signed my name this twenty-third day of May, 1919.

JAMES DE WITT HILL. 

